Am finding this entire conversation to be incredibly insightful. Performance was a major element of my focus in college! I'm starting to want to find my way back to this mindset now that I have a lot of technical elements more or less in place.

I have loved and watched these taxicab vids for over a year. I watched a number of them on the songwriting thing. Because you, as a songwriter, get can your stuff represented through these guys and they really do have contacts and in-roads to getting your music syncro to movies.
Get your songs sold to famous artists looking for new material to record, for which you get paid royalties in perpetuity.

And these guys have all sorts of good info, having been in the biz for decades in a number of capacities, from being musicians to audio engineers to producers and agents and managers. And while not decrying lessons and working on technique, they are trying to get you out of the "technique head" and into performing, using the tricks of distraction. Technique should only serve performance, not replace it. And that is why you can have a technically perfect singer botch the performance because they don't have the right feel or tone.

I am reminded of someone who did a flawless technical cover of "Like a Stone" by Audioslave. And I found it uninspiring. I mean the guy was pitch perfect. Recorded well. But his tone and style was akin to opera with a covered tone, totally the opposite of Chris Cornell's nasally whine on the original. And being so used to original, I could not help but compare. I am not saying that one should sound exactly like Cornell. But you have to find the Cornell spirit in you and let it go.

So, the cover was also a win because the cover singer did do the song in his own way. And his own way was a totally different emotional content. And that would have worked better if done with a different musical arrangement but the vocals were sung over a karaoke track of the song and that track is almost just like the original. Point being, if the song could have been arranged with different instruments and even different tempo, I would have liked the cover better as an emotional piece, rather than just a technical exercise to "prove that I can sing anything," and I just realized that last statement sounds antithetical to your website name, which is not my intention.

Granted, there is a danger in over-analysis. How to determine what is a good performance or not. Is it just another collection of techniques under the filename of performance craft? Well, yeah, there is that, too. But again, if you concentrate too much on performance craft, then you lose authenticity. Which means you have to sing a song like you mean it. But I also think you have to consider genre and where your voice sounds most authentic.

For example, you can like rock and roll while having a voice that really suits country. And do covers in a country style. And vice versa. I once heard a heavy metal version of "Ghost Riders in the Sky" that wound up being on the soundtrack of the movie, "Ghost Rider."

The most important thing said here is to find out what you are trying to communicate. When you worry about what others think of you, that is stagefright and you lock yourself up. Instead, what are you doing with the song? If you already have the technique to do high notes, then perform what should already be second nature.